The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Liquid Crystal Display (LCD) assemblies are becoming more and more common in a wide variety of products, and especially in motor vehicles such as cars and trucks. Such displays are now in widespread use in vehicle instrument panels.
In automotive and other applications, a manufacturer may wish to maintain the color of light emitted from an LCD display to within a predetermined color range or variance. For example, the manufacturer may determine that a certain shade of blue is particularly easy to see, and produces less eye strain, under a wide variety of lighting conditions that might be expected to occur inside a motor vehicle throughout the day and evening. So the manufacturer may wish that all the LCD image systems used in the instrument panels for a particular model vehicle produce a consistent color output that falls within a small color range or “window”. However, this can be challenging because variations in the construction of the LCD image systems can often cause an unacceptable deviation from the desired color range. The precise color produced by an LCD image system can vary because of small manufacturing variations in several components that are typically used in such a system, or possibly because of variations in voltage and/or currents used to operate the LCD image system. Such variation may be caused by the LCD display itself, by a light guide that is typically used in such an LCD image system, by a diffuser, or even by an LED light source used with the system. In most instances, however, it is believed that the LCD display will be the component that is predominantly responsible for producing the majority of the color shift in the output of an LCD display system, with the LED itself typically being responsible for the remaining degree of color shift. The color shifts caused by the diffuser and light guide typically are negligible.
Adding to the difficulty in compensating for the color shift produced by the LCD display is that the color shift is not consistent between LCD assemblies due to component variation; in other words the color shift has a certain tolerance along both the Cx and the Cy axes of a chromaticity graph, when plotting the variation in color output of an LCD image system on a chromaticity graph. This tolerance range significantly enlarges the area of the possible color that the output from an LCD display may take. FIG. 1 illustrates this variation. FIG. 1 shows a desired or “target” color range of an LCD image system, as defined by the square corners of line A in the chromaticity graph. In this example the target color range is a true white color, but it will be appreciated that the target color could be any selected color. The diamond shaped corners of the polygon represented by line B define the area of possible color that may be produced by a Nichia NSSW157AT, color bin b5, LED. Line C represents the “uncompensated color space”, or in other words the total area of potential color variation that may be expected from an LCD image system as a result of the range of Cx,Cy variations in color shift caused by both the manufacturing variations in the LCD display and the variations in the color output of an LED used as the light source of the LCD image system. In this example the LCD display color shift may be Cx=0.025+/−0.015, and Cy=0.05+/−0.015. So dxmin=0.01; dxmax=0.04; and dymin=0.035 and dymax=0.065. These figures produce the corners of the uncompensated color space defined by Line C.
A challenge, then, is to determine what degree/direction of color shift is needed, for each specific LCD image system, and to somehow implement that needed degree/direction of color shifting to bring the final light output of the LCD image system back within the desired color range (e.g., the color defined by line A in FIG. 1).